1. Field of the Invention
The invention relates generally to ultrasonic and radiographic medical imaging, and particularly to three-dimensional, ultrasonic mammography for the purpose of detecting and visualizing breast lesions.
2. Description of the Related Art
The standard of care for managing breast disease includes (in order) detection, diagnostic work-up, definitive diagnosis, treatment, adjuvant therapy and follow-up. In a large number of cases, the health care provider will not consider a biopsy justified and rather will opt to follow the situation with examinations every three to six months. In other cases the health care provider will typically also want to follow the progress of the lesion after adjuvant therapies are administered. This implies repeated imaging of the region of tissue containing the lesion and comparison of the earlier and later images, to detect and characterize any changes in the lesion.
Various imaging modalities are available to visualize lesions, including X-ray (most common), ultrasonography, magnetic resonance imaging and other known methods. Whatever imaging method is used, to make meaningful before/after comparisons it is necessary to insure that the same region of tissue is under examination. Preferably the tissue should be projected from the same viewing angle in both before and after images. Comparison and even interpretation of images is complicated in part because the region of interest is a three-dimensional volume, while the image is a projection onto a two-dimensional plane or planes. Three dimensional positions and relationships must be inferred or calculated, based upon the available projections. Additional difficulties result because the breast may move slightly or be slightly deformed between the earlier and later images. Even slight misalignment makes it difficult to determine whether the same lesion is comparable in earlier and later images. Even if positions, compressions and projection angle correspond well in before and after images, side-by-side comparison of complex tissue patterns is difficult, and slight changes in tissue may escape detection.